mime node: Record depth-first part numbers

This makes the part numbers readily accessible to formatters.
Hierarchical part numbering would be a more natural and efficient fit
for MIME and may be the way to go in the future, but depth-first
numbering maintains compatibility with what we currently do.

mime-node.c

@@ -112,6 +112,11 @@ mime_node_open (const void *ctx, notmuch_message_t *message,
     root->nchildren = 1;
     root->ctx = mctx;
 
+    root->parent = NULL;
+    root->part_num = 0;
+    root->next_child = 0;
+    root->next_part_num = 1;
+
     *root_out = root;
     return NOTMUCH_STATUS_SUCCESS;
 
@@ -137,7 +142,7 @@ _signature_validity_free (GMimeSignatureValidity **proxy)
 #endif
 
 static mime_node_t *
-_mime_node_create (const mime_node_t *parent, GMimeObject *part)
+_mime_node_create (mime_node_t *parent, GMimeObject *part)
 {
     mime_node_t *node = talloc_zero (parent, mime_node_t);
     GError *err = NULL;
@@ -150,6 +155,9 @@ _mime_node_create (const mime_node_t *parent, GMimeObject *part)
 	talloc_free (node);
 	return NULL;
     }
+    node->parent = parent;
+    node->part_num = node->next_part_num = -1;
+    node->next_child = 0;
 
     /* Deal with the different types of parts */
     if (GMIME_IS_PART (part)) {
@@ -267,9 +275,10 @@ _mime_node_create (const mime_node_t *parent, GMimeObject *part)
 }
 
 mime_node_t *
-mime_node_child (const mime_node_t *parent, int child)
+mime_node_child (mime_node_t *parent, int child)
 {
     GMimeObject *sub;
+    mime_node_t *node;
 
     if (!parent || child < 0 || child >= parent->nchildren)
 	return NULL;
@@ -287,7 +296,30 @@ mime_node_child (const mime_node_t *parent, int child)
 	INTERNAL_ERROR ("Unexpected GMimeObject type: %s",
 			g_type_name (G_OBJECT_TYPE (parent->part)));
     }
-    return _mime_node_create (parent, sub);
+    node = _mime_node_create (parent, sub);
+
+    if (child == parent->next_child && parent->next_part_num != -1) {
+	/* We're traversing in depth-first order.  Record the child's
+	 * depth-first numbering. */
+	node->part_num = parent->next_part_num;
+	node->next_part_num = node->part_num + 1;
+
+	/* Prepare the parent for its next depth-first child. */
+	parent->next_child++;
+	parent->next_part_num = -1;
+
+	if (node->nchildren == 0) {
+	    /* We've reached a leaf, so find the parent that has more
+	     * children and set it up to number its next child. */
+	    mime_node_t *iter = node->parent;
+	    while (iter && iter->next_child == iter->nchildren)
+		iter = iter->parent;
+	    if (iter)
+		iter->next_part_num = node->part_num + 1;
+	}
+    }
+
+    return node;
 }
 
 static mime_node_t *

notmuch-client.h

@@ -297,6 +297,13 @@ typedef struct mime_node {
     /* The number of children of this part. */
     int nchildren;
 
+    /* The parent of this node or NULL if this is the root node. */
+    struct mime_node *parent;
+
+    /* The depth-first part number of this child if the MIME tree is
+     * being traversed in depth-first order, or -1 otherwise. */
+    int part_num;
+
     /* True if decryption of this part was attempted. */
     notmuch_bool_t decrypt_attempted;
     /* True if decryption of this part's child succeeded.  In this
@@ -324,6 +331,11 @@ typedef struct mime_node {
     /* Internal: For successfully decrypted multipart parts, the
      * decrypted part to substitute for the second child. */
     GMimeObject *decrypted_child;
+
+    /* Internal: The next child for depth-first traversal and the part
+     * number to assign it (or -1 if unknown). */
+    int next_child;
+    int next_part_num;
 } mime_node_t;
 
 /* Construct a new MIME node pointing to the root message part of
@@ -356,7 +368,7 @@ mime_node_open (const void *ctx, notmuch_message_t *message,
  * an error message on stderr).
  */
 mime_node_t *
-mime_node_child (const mime_node_t *parent, int child);
+mime_node_child (mime_node_t *parent, int child);
 
 /* Return the nth child of node in a depth-first traversal.  If n is
  * 0, returns node itself.  Returns NULL if there is no such part. */